Fluid pressure-operated piston/cylinder units

ABSTRACT

The stroke of the piston of a pneumatic piston/cylinder unit is controlled by an auxiliary hydraulic piston/cylinder unit fitted to the base end of the main unit. Auxiliary piston is projected into main cylinder under static hydraulic pressure so that base position of main piston is determined by abutment with auxiliary piston. Adjustment of static pressure varies base position and hence stroke of main piston.

D United States Patent 11 1 1111 3,793,925 Collin Feb. 26, 1974 [54]FLUID PRESSURE-OPERATED 2,430,597 11/1947 Acton 92/13.1 xPISTON/CYLINDER UNITS 2,55l,246 5/1951 92/63 X 2,650,572 9/l953 92/62 X[75] Inventor: Stanley Collin, Fleckney, England 2 33 4 4 95 92/62 X[73] Assignee: Livingston and Doughty Limited, i Le'cestershlre" England3,514,950 6/1970 Davenport 1. 60/54.6 R x [22] Filed: June 15, 1972Primary Examiner-Martin P. Schwadron [21] Appl' 262,968 AssistantExaminerAbe Hershkovitz Attorney, Agent, or FirmRoberts B. Larson [30]Foreign Application Priority Data June 15, 1971 Great Britain 27906/71[571 ABSTRACT The stroke of the piston of a pneumatic piston/cylin- [52]U.S. Cl 92/13.l, 92/63 r unit i ontrolled by an auxiliary hydraulicpiston/- [51] Int. Cl. F01b 31/14, Fl5b 15/24 y n r unit fi e to he baseen of the main unit. [58] Field of Search 92/l3.10, 13.4, 15, 62, 63Auxiliary piston is projected into main cylinder under static hydraulicpressure so that base position of main [56] References Cit d piston isdetermined by abutment with auxiliary pis- UNITED STATES PATENTS ton.Adjustment of static pressure varies base position 2,244,562 6/1941Loweke 92/63 x and hence Stroke of mam Plswn' 2,358,826 9/1944 Purat92/l3.1 X 3 Claims, 1 Drawing Figure PAT ENIEn FEB26 m4 FLUIDPRESSURE-OPERATED PISTON/CYLINDER UNITS This invention relates to fluidpressure-operated piston/cylinder units, and has for its object toprovide a novel form of stop means for controlling the stroke of thepiston of a unit of this kind.

According to the invention, the stroke of a main piston/cylinder unit iscontrolled by stop means comprising an auxiliary piston/cylinder unit towhich a static fluid pressure is applied in use and which is arranged toprovide a fluid pressure-biassed stop limiting movement of the piston ofthe main unit in one direction, whereby the magnitude of the staticfluid pressure determines the stroke of piston of the main unit.

It will be appreciated that this fluid pressureoperated stop provides areadily-adjustable means of controlling the stroke of the piston of themain unit since the position at which the main piston is arrested can bevaried simply by adjusting the static fluid pressure applied to theauxiliary unit.

Primarily, but not exclusively, the invention has been devised forcontrolling the stroke of a fast-moving pneumatic piston/cylinder unit,in which case the auxiliary unit is preferably hydraulically operatedand provides for accurate control of the stroke of the main unit. It is,however, to be understood that there is no limitation in this respect.

The magnitude of the static pressure applied to the auxiliarypiston/cylinder unit may be controlled by a valve in the supply line tothe unit, or by varying the output of the pressure source, e.g., aconventional master cylinder.

Whatever means are used to control the fluid pressure, they arepreferably calibrated to indicate to an operative the position in whichthe piston of the main unit will be arrested for each particularsetting. The calibrations may be in terms of the length of stroke of thepiston or in other appropriate units depending on the use to which theunit is put.

Preferably, the auxiliary piston/cylinder unit is mounted co-axially onthe closed or base end of the main unit (i.e., the end remote from thepiston) with its piston projecting into the cylinder of the main unit sothat the stroke of the piston of the latter will be determined byabutment with the piston of the auxiliary unit. As the piston of themain unit is retracted towards the base end of the cylinder, it willmove the auxiliary piston against the action of the static fluidpressure until the force moving the main piston equals the staticpressure, when both pistons will be arrested.

In this construction, a bore will have to be provided in the base end ofthe main cylinder to receive the piston of the auxiliary cylinder.Preferably, the piston of the auxiliary unit projects through an axialbore in the base and of the cylinder of the main unit, a seal beingprovided around the auxiliary piston to prevent fluid leakage from themain cylinder.

To facilitate understanding of the invention and to enable it to bereadily carried into practice, reference will now be made to theaccompanying drawing which is alongitudinal sectional view through afluid pressureoperated stop constructed in accordance with theinvention, fitted to the base end of a main pneumatic piston/cylinderunit.

In the drawings, the main unit is generally designated 1 and has fittedto its base end 2 an auxiliary piston cylinder unit 3 which ishydraulically operated.

The main piston/cylinder unit 1 is basically of conventional form,comprising a cylinder 4 having a piston 5 slidably mounted therein.Cylinder 4 has the usual air line connections, the inlet/exhaust port atthe base end of the cylinder being indicated at 6.

Numeral 7 denotes the base end fitment of the main unit 1. Normally, thefitment is solid at its centre. However, in this embodiment, it isprovided with an axial bore 8 and with an externally screw-threaded boss9 at its outer end.

The auxiliary piston/cylinder unit 3 which forms the stop means referredto above comprises a cylinder 10 having a stepped bore 11 which isinitially open at both ends. At the end adjacent the main cylinder, thebore has an internal screw-threaded portion 12 which screws onto anexternally threaded boss 9 on the bottom end fitment 7 of the maincylinder. The opposite end of bore 11 has internal threading 13 toreceive a hydraulic coupling 14 for connection to a source of hydraulicpressure (see later).

A piston 15 is slidably mounted in bore 11, being formed with a shoulder16 which, when the piston is retracted (as illustrated), abuts againstthe step in bore 11. A return spring 17 biasses piston 5 to itsretracted position, in which the end of piston 15 inside the maincylinder 4 is flush with the inside face of the fitment 7 and henceclear of piston 5; in this position the piston can perform its fullstroke. Arranged inside a recess formed in fitment 7 is a rubber seal 18which surrounds piston 15 to prevent air leakage from the main cylinder4.

Inside the cylinder 10, a sealing cup 19 is urged by a spring 20 againstthe end of piston 15 remote from the main cylinder, the fluid pressuredelivered through coupling 14 acting on the piston through this cup.

The hydraulic pressure applied to the auxiliary piston/cylinder unit 3may be derived from any convenient source. The drawing includes a blockdiagram of a preferred arrangement; thus, a conventional master cylinderM is connected to the unit through a manuallyadjustable valve V by whichthe magnitude of the static fluid pressure can be controlled.

In use, a selected static hydraulic pressure is applied to the sealingcup 19 through coupling 14 to project the opposite end of the piston 15into the main cylinder. When the piston 5 in the main cylinder isretracted, it abuts against and moves piston 15 leftwards in the drawinguntil a position is reached at which both pistons come to rest. Thisposition is determined by the magnitude of the static fluid pressure andby the pressure exerted by the piston of the main unit and defines thestroke of piston 5. By adjusting the static pressure valve, theretracted position of the main piston and hence its stroke can beadjusted as required.

We claim:

1. In combination, a main fluid pressure-operated piston/cylinder unit,and adjustable stop means comprising an auxiliary piston/cylinder unitwhich is associated with the main unit and to which a static fluidpressure is applied in use, said auxiliary unit being adapted to providea fluid pressure-biassed stop limiting movement of the piston of themain unit in one direction, whereby the magnitude of said static fluidpressure determines the stroke of the piston of the main unit, theauxiliary piston/cylinder unit being mounted coaxially on the base endof the main unit with its piston projecting into the cylinder of themain unit so that the stroke of the piston of the latter will bedetermined by abutment with the piston of the auxiliary unit, the pistonof the auxiliary unit projecting through an axial bore in the base endof the cylinder of the main unit, a seal being provided around theauxiliary piston to prevent fluid leakage from the main cylinder, thebase end of the main cylinder being formed with an externallyscrew-threaded boss on which the auxiliary unit is mounted throughinternal screw threading at the relevant end of the auxiliary cylinder,the piston of the auxiliary unit being provided with a return springwhich, in the absence of said static fluid pressure, biasses the pistonto a retracted position clear of the main piston so that the latter canperform its normal full stroke, the end of the auxiliary piston remotefrom the main unit being provided with a sealing cup which isspring-biassed against the piston, the arrangement being such that thesaid static fluid pressure is applied to the end of the auxiliary unitremote from the main unit and acts on the auxiliary piston through theintermediary of said sealing cup.

2. Stop means according to claim 1, wherein the retracted position ofthe piston of the auxiliary unit is defined by a shoulder on the pistonwhich abuts against a step formed in the auxiliary cylinder.

3. Stop means according to claim 1, wherein the static fluid pressure isapplied to the auxiliary unit by a master cylinder which is connectedthereto through adjustable pressure control means calibrated in terms ofthe length of stroke of the main piston produced for each pressuresetting.

1. In combination, a main fluid pressure-operated piston/cylinder unit,and adjustable stop means comprising an auxiliary piston/cylinder unitwhich is associated with the main unit and to which a static fluidpressure is applied in use, said auxiliary unit being adapted to providea fluid pressure-biassed stop limiting movement of the piston of themain unit in one direction, whereby the magnitude of said static fluidpressure determines the stroke of the piston of the main unit, theauxiliary piston/cylinder unit being mounted coaxially on the base endof the main unit with its piston projecting into the cylinder of themain Unit so that the stroke of the piston of the latter will bedetermined by abutment with the piston of the auxiliary unit, the pistonof the auxiliary unit projecting through an axial bore in the base endof the cylinder of the main unit, a seal being provided around theauxiliary piston to prevent fluid leakage from the main cylinder, thebase end of the main cylinder being formed with an externallyscrew-threaded boss on which the auxiliary unit is mounted throughinternal screw threading at the relevant end of the auxiliary cylinder,the piston of the auxiliary unit being provided with a return springwhich, in the absence of said static fluid pressure, biasses the pistonto a retracted position clear of the main piston so that the latter canperform its normal full stroke, the end of the auxiliary piston remotefrom the main unit being provided with a sealing cup which isspring-biassed against the piston, the arrangement being such that thesaid static fluid pressure is applied to the end of the auxiliary unitremote from the main unit and acts on the auxiliary piston through theintermediary of said sealing cup.
 2. Stop means according to claim 1,wherein the retracted position of the piston of the auxiliary unit isdefined by a shoulder on the piston which abuts against a step formed inthe auxiliary cylinder.
 3. Stop means according to claim 1, wherein thestatic fluid pressure is applied to the auxiliary unit by a mastercylinder which is connected thereto through adjustable pressure controlmeans calibrated in terms of the length of stroke of the main pistonproduced for each pressure setting.